1. Field of the Invention
The present invention relates to an imaging device which captures an image of a photographic subject which is formed by an imaging optical system such as a lens, by an imaging element, and an imaging device which is used in an environment in which a temperature variation is large.
2. Description of the Related Art
An imaging device which captures an image of a photographic subject which is formed by an imaging optical system such as a lens, by an imaging element, has become popularized. The imaging device is used in equipment, the main function of which is photographing, such as a digital camera or a digital video camera, and in addition, an imaging device (a camera module) is also additionally mounted in a mobile phone, a smart phone, a PDA, a notebook type personal computer, or the like according to the downsizing of the imaging device. In addition, the imaging device is also in widespread use as a monitoring camera which is installed outdoors, or a car-mounted camera which is mounted on a moving body (for example, an automobile, a motorcycle, a bicycle, a ship, or an aircraft) for travel recording, support of parking in a garage, or the like.
Although the imaging devices are used in various locations in this manner, in particular, in an imaging device which is used in a harsh environment in which a temperature variation is large, such as the car-mounted camera, it is required to exhibit stable performance regardless of the expansion or the contraction of each portion configuring the imaging device. For example, in a case where an imaging device which does not have a focus adjustment function is assembled such that a focal position is fixed in a normal-temperature environment (for example, an environment of about 20° C.), if the imaging device is used in a high-temperature environment (for example, an environment of about 80° C.), focus movement may occur due to the expansion of a lens or a lens barrel holding the lens, and therefore, it is preferable to compensate for the focus movement due to a temperature variation.
JP2004-147188A discloses a digital camera in which an expanding and contracting member which expands and contracts according to temperature is provided on the rear surface of an imaging element. In this digital camera, in a case where a temperature variation occurs, the position of the imaging element is automatically finely adjusted by the expansion and the contraction of the expanding and contracting member, thereby compensating for focus movement.
JP2008-304641A discloses a car-mounted camera for infrared photographing in which focus movement due to a temperature variation is suppressed by forming a lens barrel into a double structure composed of an outer cylinder and an inner cylinder. Specifically, the car-mounted camera of JP2008-304641A has a structure in which a base end of the outer cylinder is fixed to a support integrated with an imaging element and the tip of the outer cylinder is fixed to the tip of the inner cylinder, and is made such that a focal position is maintained on the imaging element even in a temperature variation by offsetting the shift of the focal position due to the expansion to the photographic subject side of the lens barrel (the expansion of the outer cylinder) on the basis of the support and a change in the refractive index of a lens due to the expansion from the tip of the outer cylinder to the imaging element side (the expansion of the inner cylinder) by adjusting the materials (the thermal expansion coefficients) and the lengths of the outer cylinder and the inner cylinder.
Further, JP2008-211780A discloses an imaging device in which a lens barrel has a double structure composed of a lens holding unit (an inner cylinder) and an intermediate member (an outer cylinder) and the mounting position of the lens holding unit with respect to the intermediate member can be changed to have three predetermined positions, and discloses a technique in which in a case where focus movement occurs due to a temperature variation, the focus movement due to a temperature variation is suppressed by changing the mounting position of the lens holding unit.